This invention relates to battery electrodes and more particularly to light weight sintered nickel battery electrodes.
The nickel composite electrode disclosed in U.S. Pat. No. 4,215,190 entitled "Lightweight Battery Electrode," which issued to William A. Ferrando and Raymond A. Sutula on July 20, 1980, has proven its advantage over conventional powder electrodes in reducing battery weight and bringing higher energy density without sacrificing durability and cycle-life. However, it suffers from one major drawback, i.e., a slow increase of active material utilization with cycling. Typically it takes 40-80 cycles to reach 90% utilization. This kind of slow formation has been identified as the single remaining barrier to the practical use of the composite electrode. Under similar impregnating conditions, powder-sinter electrode would not experience such a behavior. Conventionally sintered nickel electrodes are loaded with nickel hydroxide active material by chemical or electrochemical impregnation method. In either method about 5-7% (weight percentage) of cobalt hydroxide is added to the active material by coprecipitation from a same bath. Ferrando et al. (U.S. Pat. No. 4,215,190) used these conventional procedures to load their nickel phosphorous coated carbon fiber grid electrodes. William A. Ferrando in U.S. patent application Ser. No. 740,115, filed on May 29, 1985, entitled "Method of Impregnating Active Material into Composite Nickel Plaque," discloses a method which uses a suspension of fine particles of nickel active material (e.g., Ni(OH).sub.2) and a cobalt additive (e.g., Co(OH).sub.2) in ethylene glycol to impregnate the nickel-coated graphite fiber plaque. This method greatly reduces the cost of filling the plaque with nickel active material and cobalt compound; unfortunately, here as with the conventional methods from 40-80 cycles are required to reach the level of 90 percent utilization.
British Pat. No. 777,417 entitled "Improvements in or Relating to Process for Activating Positive Electrodes of Alkaline Accumulators," which issued to Hans Winkler on June 19, 1957, discloses a process in which a nickel hydroxide/nickel powder sintered electrode is soaked in a cobalt sulfate solution and then an alkali metal carbonate solution which causes cobalt hydroxide to precipitate out onto the nickel active material. Disappointingly, when this method is applied to nickel hydroxide/sintered nickel-coated graphite fiber electrodes, with their much longer pores, the treated electrodes still require from 25 to 30 charge-discharge cycles to obtain 90 percent of capacity.
Thus, it remains to find a method of reducing the number of charge-discharge cycles required to bring the cells up to 90 percent of capacity.